The invention relates to a device for conveying a motion picture film.
From German Patent Application No. DE 44 18 471 A1 a motion picture film recording camera is known for the exposure and intermittent conveyance of a motion picture film which is perforated along one or both sides. The unexposed motion picture film mounted in a film cassette connected to the camera housing of the motion picture film recording camera enters through an opening into the camera housing of the motion picture film recording camera and then leaves through this opening as exposed film. The feed of the motion picture film consists of one or more film conveying toothed reels which move the motion picture film continuously whilst a film feed mechanism moves the motion picture film intermittently past a picture window where it is covered in the transport phase through a rotating aperture and released for exposure during the exposure phase. In order to balance the continuous film movement and intermittent film movement film loops are formed on either side of the picture window.
The rotating aperture consists of an aperture disc which is either driven by an aperture motor which is coupled electrically to the film conveying or camera motor of the film drive so that the speeds of the aperture motor and of the camera motor run synchronously, or a direct mechanical coupling is provided where the rotating aperture is coupled to the camera motor through a film conveying gear.
The film feeding mechanism contains a film guide and a plunge gripper switch mechanism with a transport gripper which is moved by a gripper gearing so that its at least one transport gripper point during the intermittent conveyance of the motion picture film describes a closed crank loop where the transport gripper point first projects into the film perforation, implements the film transport step, moves back out of the film perforation and returns to its starting position. At the reversing points of the crank loop of the transport gripper the locking gripper point of a locking gripper correlated with the movement of the transport gripper and describing an oscillation movement engages in the film perforation, undertakes any possible correction of the alignment of the motion picture film in the film plane and secures the picture position of the motion picture film during the exposure of the film frame. After exposure of the film frame of the motion picture film the locking gripper point is again withdrawn so that the motion picture film is released for a further film transport step by the transport gripper.
In order to enable a greater exposure clearance during exposure of the motion picture film or a greater brightness performance during playback of the motion picture film the gripper gear contains two gear shafts moved in the same rotational direction of which one gear shaft has n-times the angular speed compared with the other gear shaft and the light sector of the aperture disc is either variable proportional to the angular speed or the diameter of the aperture disc is selectable inversely proportional to the angular speed and the centre point of the aperture is shifted relative to the picture window with decreasing diameter of the aperture disc.
It is known to move the motion picture film for exposure or projection of a film image depending on the desired image format either by three or four perforation holes of the single or double-sided film perforation during one film transport step and thus through different lateral conditions of the image formats and with film transport steps by three perforation holes to obtain a 25% greater utilisation of the film material used.
From German Patent Publication No. DE 690 24 048 T2 a toothed reel structural assembly is known for adapting a film projector to film transport steps by three or four perforation holes per film frame wherein the toothed reel connected to a drive shaft consists either of a cylindrical inner sleeve with teeth engaging in the film perforation or of a cylindrical outer sleeve likewise with teeth engaging in the film perforation and insertable on the cylindrical inner sleeve. With the same speed of drive shaft and the same toothed spacing but different diameter of the inner sleeve and outer sleeve four/three times as much motion picture film is transported with the outer sleeve than when using the inner sleeve with the outer sleeve removed so that the outer sleeve is designed suitable for film transport steps by four perforation holes per film frame and the inner sleeve for film transport steps about three perforation holes per film frame.
The known toothed reel structural assembly can indeed be used in a film projector which is equipped solely with toothed reels for the continuous and for the intermittent film transport with selectively three or four perforation holes per film picture. It cannot however be used for the following reasons, or at least not without limitations, for the film transport by selectively three or four perforation holes per film picture in a motion picture film recording camera, as in the motion picture film recording camera known from German Patent Application No. DE 44 18 471 A1 with film toothed reels for the continuous film conveyance and with a gripper feed mechanism for intermittent film conveyance.
With a film conveyance step of four perforation holes per film frame the transport gripper conveys the motion picture film during one revolution of the camera motor by four perforation holes each time whereby the unwinding toothed reel drawing the motion picture film out from the film cassette and the winding toothed reel conveying the motion picture film again into the film cassette execute one revolution about four toothed spacings each time. If the toothed reels each have 16 teeth then they consequently turn one quarter of the drive shaft of the camera motor driving the gripper feed mechanism. Compared to this the transport gripper with a film conveyance step about three perforation holes per film frame conveys the motion picture film three perforation holes for each revolution of the camera motor. To maintain constant film loops to compensate for the intermittent and continuous film conveyances it is necessary therefore in the case of a camera motor driving both the gripper feed mechanism and the toothed reels to change the translation ratio for driving the toothed reels so that these only turn by three teeth during one revolution of the gripper drive shaft and draw off a corresponding film length from the film cassette and feed it into the film cassette.
A use of the toothed reel structural assembly known from German Patent Publication No. DE 690 24 048 T2 in a motion picture film recording camera with a gripper feed mechanism would therefore make it necessary to re-equip the winding toothed reel and unwinding toothed reel or alternatively to replace the film transport gear for driving the toothed reels or by replacing gear elements such as belts and gear wheels to adapt it to the changed speed of the camera motor. For this however it would be necessary to dismantle the entire inner camera of the motion picture film recording camera or parts thereof, more particularly the camera electronics which involves considerable expense and additional costs.
The object of the present invention is therefore to adapt the device mentioned at the beginning to a film conveyance of three or four perforation holes per film frame without exchanging the film conveyance gearing or the winding and unwinding toothed reels or changing the geometry of the winding and unwinding toothed reels.